Seemingly there is a trick that allows replays: DO NOT MOVE any units in the deployment phase, just start battle immediately.

Regularly replays don't work since it is caused with max number of men per unit which seems cannot be over vanilla's 160 or 180 depending on campaign while FotE increases that numbers up to 240 men.
The same happens to most major mods incl. DEI, so trick can be probably used for every overhaul there.